In typical windows of the tilt-in type, exemplified in U.S. Pat. No. 3,959,926 to M. V. Noecker et al and U.S. Pat. No. 3,861,082 to M. L. Dau, the sliding sash members are pivotally slidably retained in the associated window frame side rails at their bottom ends and are slidably retained in the side rails at their top ends by retractable bolt elements. The side portions of the sash are provided with weather-strips which normally sealingly engage against vertical flange elements on the associated frame side rails. When the sash, whose framing portions are usually made of extruded aluminum, plastic, or other relatively flexible material, is subjected to heavy external wind forces, the sash tends to bow inwardly at its center portion, and this inward distortion is frequently of sufficient magnitude to cause the associated weather-stripping to disengage from the said rail flange elements, thereby allowing leakage of air past the weather-stripping; this is a particularly severe problem with PVC. Sometimes such heavy external wind forces can even cause permanent distortion of the sash. This undesirable contingency may occur either where the weather-stripping is carried by the sliding sash members and normally engages the stationary side rails of the associated window frame, or in the reverse situation where the weather-stripping is mounted on the stationary window frame side rails and normally engages the sliding sash members. In either case there is a need for controlling and limiting the bowing of the sash members under heavy wind forces.
A preliminary search of the prior art reveals the following U.S. Pat. Nos. of interest:
Hagerty et al, 2,763,038 PA0 Livsey et al, 2,933,777 PA0 Dau, 3,861,082 PA0 Noecker et al, 3,959,926 PA0 Wolfe, 4,087,941